Gas-lift operations may be employed in hydrocarbon wells as a primary recovery technique for lifting fluids, such as water or oil, from the well. One type of gas-lift operation comprises injecting gas downwardly from the surface into the well bore annulus formed between production tubing and the well bore wall or casing. As the gas is injected from the surface, it gradually reduces the density of the column of fluid in the well from top to bottom. As the density of the fluid is reduced, the fluid becomes lighter until the natural formation pressure is sufficient to push the fluid up and out of the well through the production tubing, typically through gas-lift valves disposed at spaced locations along the production tubing.
Using this gas-lift method, a completed well that is ready to be placed on production, for example, may be unloaded of water to thereby remove the hydrostatic head created by the water and enable the flow of the lighter produced hydrocarbons from the formation into the well bore. When gas-lift valves are employed to unload the well, the well bore annulus may be packed off below the gas-lift valves to reduce the volume of fluid that must be lightened by the gas and unloaded through the valves. The gas-lift valves close sequentially from top to bottom automatically when the fluid has been lifted out through the production tubing and injection gas remains in the well bore annulus at that depth. By this means, each succeeding lower gas-lift valve is closed as the fluid level in the annulus is successively lowered until the lowermost gas-lift valve is exposed to the injection gas in the annulus. Thereafter, gas lift does not occur below the packer, but because the well bore annulus has been unloaded above the packer, the natural formation pressure may be sufficient to push the column of produced fluid up and out of the well through the production tubing.
The above-described method may be sufficient for gas-lifting a standard length well. However, this method may be ineffective to gas-lift long, multi-zone or deviated production wells. In particular, a high pressure gas would be required to sufficiently lighten a very long column of fluid. However, it is undesirable to inject high pressure gas into the annulus because such gas would overcome the formation pressure and inject into the perforations, thereby preventing production fluids from flowing into the well.
Gas-lifting operations for long, multi-zone or deviated production wells may be improved by using a production packer to seal the well bore annulus so that the well above the packer may be unloaded to thereby reduce the hydrostatic head. However, because gas cannot be injected below the packer, and because the packer must be set above the perforated zone, even using a packer may be insufficient to effectively gas-lift a well down to the last production interval when the well bore extends some distance beyond the packer.
Other types of gas-lift operations exist, such as, for example, an inner string extending from the surface through the production tubing to inject gas into the fluid in the production tubing, but such apparatus and methods can be cost prohibitive. Therefore, a need exists for apparatus and methods to effectively gas-lift a long, multi-zone or deviated production well. In particular, a need exists for apparatus and methods that enable gas injection directly to the perforated zone below the production packer, and a cost-efficient method of unloading a well bore below a production packer.